Re: [Qemu-devel] [PATCH V7 23/24] apci: fix PXB behaviour if used with unsupported BIOS

[Laszlo Ersek]

On 06/01/15 15:05, Marcel Apfelbaum wrote:
> On 06/01/2015 03:27 PM, Michael S. Tsirkin wrote:
>> On Mon, Jun 01, 2015 at 03:21:19PM +0300, Marcel Apfelbaum wrote:
>>> On 06/01/2015 03:17 PM, Michael S. Tsirkin wrote:
>>>> On Mon, Jun 01, 2015 at 01:40:19PM +0200, Gerd Hoffmann wrote:
>>>>> On Mo, 2015-06-01 at 12:44 +0300, Marcel Apfelbaum wrote:
>>>>>> On 05/31/2015 09:12 PM, Michael S. Tsirkin wrote:
>>>>>>> On Mon, May 25, 2015 at 06:34:01PM +0300, Marcel Apfelbaum wrote:
>>>>>>>> PXB does not work with unsupported bioses, but should
>>>>>>>> not interfere with normal OS operation.
>>>>>>>> We don't ship them anymore, but it's reasonable
>>>>>>>> to keep the work-around until we update the bios in qemu.
>>>>>>>
>>>>>>> We already did, did we not?
>>>>>> Yes, we did, but Gerd preferred to keep this patch around.
>>>>>> Adding him to thread.
>>>>>
>>>>> seabios bundled with qemu isn't the only possible firmware.
>>>>>
>>>>> We have ovmf, coreboot, qboot.
>>>>
>>>> ovmf is especially interesting. Marcel, did you look at what
>>>> happens with pxb and ovmf?
>>> No, I talked to Laszlo about it, he said ovmf is not there yet.
>>> OVMF will not query the extra buses, so the devices on the extra bus
>>> will not be visible.
>>> Adding him to the thread.
>>>
>>> Thanks,
>>> Marcel
>>
>> But does OVMF need this specific patch?
> I don't think so because more than likely it doesn't scan for the extra
> buses,
> so it will not try to configure these devices.
> Laszlo, am I right?

Well, I don't know. :)

First, I'm not seeing the specific patch in question (can you pls send
me a URL into the web archive, or a Message-Id?)

Second, recently I tested OVMF on Q35, but not just with a simple /
usual command line invocation -- I tested it on a Q35 machine configured
by libvirt. That's a very different animal.

While it exposed a problem in OVMF's own boot order processing:

https://github.com/tianocore/edk2/commit/feca17fa4b

I was surprised to see that the PCI bus driver enumerated devices behind
two bridges no less without any problems. So, bridges off the one root
bridge should work, but several root bridges probably won't. (Exposing
root bridges is the responsibility of another driver, and they are not
enumerable in the usual way.)

Thanks
Laszlo